The present invention relates to a silver halide color photographic element containing a magenta or cyan dye-forming coupler, and in particular a fused ring heterocyclic dye-forming coupler capable of carrying a photographically useful group.
In silver halide based color photography, a typical photographic element contains multiple layers of light-sensitive photographic silver halide emulsions coated on a support with one or more of these layers being spectrally sensitized to each of blue light, green light and red light. The blue, green and red light-sensitive layers typically contain, respectively, yellow, magenta and cyan dye-forming couplers, hereinafter xe2x80x98couplersxe2x80x99. These couplers provide yellow, magenta and cyan dyes in the so-called subtractive color process to reproduce their complementary colors blue, green and red as in the original image. After exposure to light, color development is accomplished by immersing the exposed material in an aqueous alkali solution containing an aromatic primary amine color developing agent. The couplers are selected so as to react efficiently with the oxidized color developing agent so formed, thereby minimizing the amounts of coupler and silver halide necessary in the photographic element
A variety of coupler types have been used in photographic materials. Among the known couplers are cyclic azoles, in particular those containing bridgehead nitrogen 5,5; 5,6 or 5,5,6 fused ring systems, such as pyrazolotriazoles, pyrazolotriazines, pyrazolopyrimidines, pyrazolothiadiazines, pyrrolotriazoles, imidazopyrazoles and pyrazolobenzimidazoles, for example as described in EP-A-0 119 860, EP-A-0 269 436, EP-A-0 398 664, EP-A-0 714 892, EP-A-0 744 655, EP-A-0 802 454, EP-A-0 883 024, U.S. Pat. Nos. 4,916,051, 4,950,585, 4,970,142, 5,451,501, 5,776,669 and 6,132,945 and JP 04125557. These couplers may form magenta or cyan dyes depending on the ring structure and substituents.
A coupling-off group is a group adapted to split off from the coupler as the result of the reaction between the coupler and the oxidation product of an arylamine color developing agent. Coupling-off groups can determine the equivalency of the coupler, can modify the reactivity of the coupler or can, where required, advantageously affect the layer in which the coupler is coated or other layers in the element by performing, after the release from the coupler, such functions as development inhibition, development acceleration, bleach inhibition, bleach acceleration or color correction. Typical examples of coupling-off groups include, for example, halogen, alkoxy, aryloxy, sulfonyloxy, acyloxy, phosophonyloxy, heterocyclyloxy, acyl, heterocyclyl, sulfonamido, benzothiazolyl, alkylthio, arylthio, heterocyclylthio and arylazo groups. These coupling-off groups are described in the art, for example, in U.S. Pat. Nos. 2,455,169, 3,227,551, 3,432,521, 3,467,563, 3,617,291, 3,880,661, 4,052,212 and 4,134,766; and in UK Patent Nos. and published applications 1,466,728, 1,531,927, 1,533,039, 2,066,755A and 2,017,704A, the disclosures of which are incorporated herein by reference.
However the number of coupling-off group moieties which form good couplers in combination with fused ring heterocyclic systems, such as for example pyrazoloazoles, is limited. A commonly used coupling-off xe2x80x98groupxe2x80x99 for these systems is a chloro atom, as described, for example, in U.S. Pat. No. 5,681,691. Whilst arylthio groups are disclosed in U.S. Pat. No. 5,262,292 as acting as good coupling-off groups for pyrazolone couplers, they do not act as such for fused ring heterocyclic systems, even when a solubilising group such as a carboxylic acid is present. Couplers containing heteroarylthio coupling-off groups, wherein the coupling-off group functions as an inhibitor, include mercaptothiadiazoles, mercaptooxadiazoles or, as disclosed for example in JP 05127326, mercaptotetrazoles. Being inhibitors these heterocycles affect development and couplers containing them are xe2x80x98Development Inhibitor Releasingxe2x80x99 couplers (DIRs). Couplers wherein the coupling-off group functions as a bleach accelerator are disclosed, for example, in EP-A-0 287 073.
There is a need for coupling-off groups for fused ring heterocyclic ring systems having at least one bridgehead nitrogen atom which can confer satisfactory activity on the couplers and which can comprise or be linked to photographically useful groups (PUGs), such as dyes, development accelerators and electron transfer agents, without the coupling-off group having an inhibitory effect on silver development or causing a bleach acceleration effect. Whilst a chloro coupling-off group on such couplers provides the necessary activity, it is not possible to link a PUG thereto. Although a PUG can be linked to an arylthio coupling-off group, for the fused ring heterocyclic ring systems above a coupler including such a group is not sufficiently active for practical use.
It has now been found that, when a heterocyclylthio coupling-off group is linked to a heterocyclic coupler containing at least two fused rings and having at least one bridgehead nitrogen atom, not only does the resulting coupler possess the required activity but the heterocyclylthio moiety released upon reaction with oxidized developer does not significantly inhibit silver development nor cause a bleach acceleration effect.
According to the present invention therefore there is provided a photographic element comprising at least one light-sensitive silver halide emulsion layer having associated therewith a heterocyclic magenta or cyan dye-forming coupler of formula (I), 
wherein
HET is a heterocyclic coupler comprising at least two fused rings and having at least one bridgehead nitrogen atom;
S is bonded to a position of HET capable of releasing the heterocyclylthio moiety from HET upon reaction with oxidized developer;
X is a heteroatom selected from nitrogen, oxygen and sulfur, bonded to the carbon atom bearing the exocyclic S and to other ring atoms only; and
Z are the atoms necessary to complete an unsubstituted or substituted heterocyclic ring or ring system, which may contain one or more other heteroatoms selected from nitrogen, oxygen and sulfur;
provided also that the heterocyclylthio moiety released upon reaction with oxidized developer does not significantly inhibit silver development nor cause a bleach acceleration effect.
In another embodiment of the invention there is provided a multi-color photographic element comprising a support bearing yellow, magenta and cyan image-dye-forming units comprising at least one blue-, green- or red-sensitive silver halide emulsion layer having associated therewith at least one yellow, magenta or cyan dye-forming coupler respectively, wherein the element includes a heterocyclic magenta or cyan dye-forming coupler of formula (I) as herein described.
In yet another embodiment of the invention there is provided a process of forming an image in a photographic element as hereinbefore defined after the element has been imagewise exposed to light, comprising contacting the element, as herein described, with a color developing agent.
In addition to the couplers herein described having the required activity, the heterocyclylthio coupling-off groups can comprise or be linked to PUGs, such as dyes, development accelerators or electron transfer agents, thereby providing a practical way of attaching these groups to fused heterocyclic ring systems.